This research guide explains how litigators find, plead, and prove inequitable conduct in patent prosecution, and how patent owners defend against it. It works through the heightened pleading standard of Exergen Corp. v. Wal-Mart Stores under Federal Rule of Civil Procedure 9(b), the two-element Therasense test of but-for materiality and specific intent to deceive, and the duty of candor codified at 37 C.F.R. Section 1.56. It maps the concrete sources of proof a litigator mines — file wrappers, information disclosure statements, foreign counterparts, sworn declarations, and assignment records — and lays out discovery sequencing, the crime-fraud exception, prosecution bars, expert practice, and the clear-and-convincing burden at trial. Fresh worked hypotheticals show how materiality and intent are actually assembled from a documentary record. A closing FAQ answers the questions clients ask most, and the whole guide is written so a judge, a practicing lawyer, and an inventor can each follow it.